Field of the Invention
The present invention relates to a stitchless steering wheel fitted with leather. More particularly, to a technology of covering a steering wheel with leather, by fitting the leather into the steering wheel by using rim bezels and the like instead of sewing the leather.
Description of Related Art
In general, hand sewing is applied to cover a steering wheel for a vehicle with leather.
The hand sewing is carried out nearly completely manually when covering the steering wheel with leather.
As an example, the hand sewing process is carried out in the order of operations of testing raw fabric→cutting→sewing/punching (punching for connecting and sewing leather)→attaching a double-sides tape→cleaning surfaces (removing foreign substances)→applying adhesives→attaching leather→sewing→supplying hot air (removing wrinkles on the surface)→completing the covering operation.
Since hand sewing is carried out nearly completely manually, there is a problem in that a large amount of cycle time is needed.
Meanwhile, if stitch intervals are increased to reduce the cycle time required for the sewing, a deterioration of external appearance (i.e., separation of leather, low quality, and the like) occurs. Additionally, grip feeling when a driver holds the steering wheel is degraded because of unevenness of sewed line portions (displeasure when rotating and returning the steering wheel).
The process of supplying hot air is carried out to forcedly contract the leather in order to remove wrinkles after covering the steering wheel with the leather, but because of damage to a leather surface caused by a high temperature, problems such as deterioration in durability condition, discoloration of leather, and peeling off of leather occur.
One steering wheel typically has 400 to 450 stitches, and a cost required for sewing leather is about 24% of an overall price of manufacturing the steering wheel.
Some automakers sometimes use a method of fitting leather (stitchless) instead of hand sewing in order to solve the problems with the hand sewing, but because of the following problems, the method are rarely used.
First, because of deformation in polyurethane (PU) foam, deterioration in adhesive force of an adhesive, contractile force caused by contraction of leather, and the like, there is a problem in that leather is separated from a leather fitting groove and the leather peels under a high temperature condition.
Second, during the process of supplying hot air in order to remove wrinkles of leather, the leather peels due to contraction of the leather, and as a result, there is a problem in that a defect rate is increased in the manufacturing step.
Third, the leather is matched with a PU material with low hardness, which causes a collapse at an edge portion, such that a leather matching portion is separated due to contraction of the leather after the process of supplying hot air and the process of conditioning durability/heat-resistance, and as a result, a defect of an external appearance of the leather matching portion occurs.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.